1. Field of the Invention
The invention relates in general to an optical scanner, and more particularly, to an optical scanner that may assemble different lens designs for changing focus and resolution.
2. Description of the Related Art
The conventional optical scanner (referring to FIG. 1) comprises a light source 100, a reflection compound mirror 400, an object lens 500 and an optical sensor, such as a charge coupled device (CCD) 600. While scanning, the light source 100 radiates on the document 200, an image light is obtained via reflection or transmission. The reflection compound mirror 400 is comprised of several reflection mirrors (401, 402, 403) located along the optical path. Therefore, the image of the document 200 is incident to the reflection compound mirror 400. Being reflected by the reflection compound mirror 400, the image is transmitted to the objective lens 500. The objective lens can receive the image of the document 200 transmitted from the reflection compound mirror 400, and display such image in the charge coupled device 600.
The conventional objective lens is designed by simulation software according to the requirements of resolution, total track (TT), magnification and modulation transfer function (MTF) provided by the client. The factors of lens, material, curvature, number of lenses, size, and length of the objective lens are thus determined. The sample is then fabricated, and the inspection of the sample and simulation are performed. For example, the objective lens 502 of 600 dpi as shown in FIG. 2a is normally formed of three lenses. The objective lens 504 of 1200 dpi as shown in FIG. 2b is normally formed of four lenses.
According to the above, the conventional design of the objective lens has to meet the specification requirements including the resolution, the total track, the magnification and the modulation transfer function. For different specification requirements, a new objective lens has to be designed. Alternatively, the specification of the current optical scanner has to be changed.